1. Field of the Invention
The invention relates to direct broadcast satellite systems, and particularly to improvements in aperture and method for collector alignment.
With the advent of consumer satellite receivers, particularly satellite receivers having inexpensive small aperture collectors intended for optional installation by the user, it is of paramount commercial importance that the collector (and associated elements) be capable of being quickly, easily, and inexpensively aligned with a satellite whose transmission is to be received.
Because of the small aperture of such collectors, they are necessarily designed to have high gain, making precise alignment especially critical. For example, 18-inch diameter offset-fed parabolic reflectors are used in present commercial systems, having a 3 dB beam width of only approximately 2 degrees. Low cost precise alignment of such collectors in a consumer environment has been challenging. Accurate aiming of such satellite collectors is of significance especially in areas of the signal-receiving territory where rain fade is a problem. The more precise the aim of the satellite collector, the less serious is the rain fade problem, and the shorter its duration.
Existing satellite collector alignment equipment capable of precisely aligning such collectors is expensive and requires the services of a professional installer. Installation equipment which is capable of precisely aligning such satellite collectors, and yet which is affordable and readily useable by installers and even by the consumer is not available at present.
To align such a satellite collector for maximum receiver signal strength using today's methods, the satellite is pointed in the approximate direction of the satellite whose transmission is to be received. The collector is then adjusted in azimuth and elevation while the level of the received signal is monitored in search of a "peak". In practice, however, it has proven difficult to "peak" the received signal because the signal level meter comprising part of the satellite receiver typically has a non-linear response at the normal high "peak" signal levels. This non-linear response at the desired levels can mask the effect of small non-alignments, making them difficult for the user to notice. As a result, finding an exact orientation of the collector for peak signal reception is not readily achieved.
2. Description of Related Art
U.S. Pat. No. 4,888,596 discloses a method and apparatus for determining earth station parameters such as rain margin. The '596 technique utilizes a series of radiation attenuating pads which are manually held, or supported in a box-like holder, adjacent to a receiving horn. The pads attenuate radiation focused by a satellite dish on the horn. The attenuating pads are stacked one at a time in front of the horn while a service attendant watches a connected television receiver until "sparklies" appear on the television screen. The attenuation produced by the pads is logarithmically additive. When the sparklies are observed, the antenna orientation is then adjusted until the pattern of sparklies is minimized. The attenuation figure thus derived is used as a measure of the rain margin for the satellite communication system.
The approach of the '596 patent suffers from a number of drawbacks. First, it is cumbersome and slow in use, and not susceptible to being automated. With the method of the '596 patent, it would be difficult for an installer to determine signal peaking by observing the number or strength of the sparklies on the screen. It is not readily adaptable for use with digital transmissions (such as digital DBS transmissions), as images displayed of digitally transmitted signals do not degrade gradually or produce visible noise-like phenomena on a television screen which could be monitored to determine an acceptable minimum signal strength. Further, the attenuating pads must be maintained in sealed bags to prevent their degradation. Repeated use may therefore lead to damage and deterioration of the pads, reducing accuracy, convenience, and reliability. The adjustments in attenuation produced by the stacked pads are limited in resolution to a few discrete values, and continuous changes in the amount of attenuation of the incoming satellite signal are not possible. The '596 method thus suffers from lack of precision in determining the optimum satellite collector position.